In recent years, a network technique for searching for a device which provides a predetermined service on a network has been developed. As one example of this technique, Microsoft Corporation proposes UPnP (Universal Plug and Play) (Universal Plug and Play Device Architecture Version 1.0, 8 Jun. 2000 10:41 AM). UPnP defines a “service”, “device”, and “control point”. The service is a logical unit for providing a predetermined service, the device is a logical unit including one or more services, and the control point is a logical unit for controlling the one or more services. The device and control point defined by UPnP will be called an “UPnP device” and “UPnP control point”.
The UPnP device and the UPnP control point notify of and detect the service and the like by using SSDP (Simple Service Discovery Protocol). The service and the like are notified by transmitting a discovery message which includes the URL of a device description file in XML (Extensible Markup Language).
When connecting to an UPnP network, the UPnP device acquires an IP address from a DHCP server on the network, and multicasts the pieces of information of the type and service of the device as an ssdp:alive message on the network. For example, when the UPnP device serves as a VTR, the device describes and transmits the pieces of information of the type of an available recording medium, recording format, playback function, and the like in the XML. The pieces of information of the corresponding recording medium and recording format are defined as state variables, and the function of operating the devices, e.g., a playback function is defined as an action. When the UPnP device is disconnected from the UPnP network, it is recommended to multicast an ssdp:byebye message which notifies of the disconnection. Note that the ssdp:alive message describes the term of validity of the UPnP device and service which are notified by the ssdp:alive message. When the ssdp:byebye message is not transmitted, the UPnP control point disables the corresponding service and the like after the term of validity described in the received ssdp:alive message.
Furthermore, data communication on a wireless network between PCs and cellular phones has rapidly prevailed. Such wireless networking is sweeping into digital devices, and all of the digital devices are connected by mixing the wired and wireless techniques.
In the above-described arrangement, assume that a digital camera and digital video camera are simultaneously connected to the network with a plurality of devices. When the user tries to select a specific printer from the plurality of digital devices, the user can only acquire pieces of information of many devices on the network, and find to select the specific printer from the acquired pieces of device information. Therefore, as the number of the connected devices increases, selection of the specific device from the plurality devices is increasingly troublesome for the user.